Methods were developed for measuring single stranded and duplex DNA by electrospray ionization mass spectrometry. Mass spectrometric analysis of DNA was found to be sensitively dependent on the nature of cations in the spray solution, the ionic strength of the spray solution, and conditions within the electrospray ion source. Investigation and observation of non-covalent interactions between DNA strands in the gas phase by ESIMS from high organic solvent. The DNA was a 14mer duplex. The complex observed was a homodimer between two top strands of the DNA (Joe Kim/Burley).